Liquid crystal display

ABSTRACT

A liquid crystal display is provided that includes a first substrate including a thin film transistor and a storage capacitor, a second substrate including a color filter layer with a recess at a location opposite to the storage capacitor, a common electrode on the color filter layer, and a liquid crystal layer between the first and second substrates. Spacers are provided between the first and second substrates to maintain a gap therebetween. In regions that include the storage capacitor, the recess compensates for a height difference in layers forming the capacitor on the first substrate to maintain a substantially uniform liquid crystal layer thickness over the whole region of the liquid crystal display, and thus provides a high quality picture.

This application claims the benefit of Korean Patent Application No. P2000-38014, filed on Jul. 4, 2000, which is hereby incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a LCD (Liquid Crystal Display), andmore particularly, to an LCD having a balanced layer of liquid crystal.

2. Background of the Related Art

Thin-film transistor liquid crystal displays (TFT-LCD's) are widely usedas display elements for LCD TVs, notebook PCs, LCD game machines,projection TVs, high definition TVs (HD-TVs), and the like. Recentinterest in flat panel displays has led to the development of flat panelTFT-LCDs, and demand for these devices is steadily increasing. Thedevelopment of TFT-LCD's and their applications are driven, andsometimes accelerated by a desire for display panel size increase and/orenhanced resolution. Accordingly, there have been ceaseless efforts tosimplify the fabrication process and improve manufacturing yields ofTFT-LCDs to attain increased productivity at low cost.

Unlike a Plasma Display Panel (PDP) or a Field Emission Display (FED),an LCD requires back lighting to illuminate the display screen. The backlight is a light source that is provided to transmit light through aplurality of separately controllable liquid crystal pixels formed in theLCD. In operation, the transmissivity of light from the light source isvaried in accordance with voltages applied across electrodes provided oneither side of the liquid crystal. The transmissivity through a pixelmay be varied independently for each pixel utilizing electroopticproperties of the liquid crystal injected inside the panel. The liquidcrystal directs the light from the back light to display an image on theLCD panel screen according to a pattern of pixels that are charged witha voltage.

FIG. 1 is a simplified plan view of an LCD layout the related art.Referring to FIG. 1, the related art LCD includes a plurality of gatelines 11 formed at fixed intervals and data lines 13 formedperpendicular to the gate lines 11. At each intersection of the gatelines 11 and the data lines 13, a TFT is provided for controlling avoltage charged to an LCD pixel associated with the TFT. Each TFTincludes a gate electrode 11 a extending from the gate line 11, sourceand drain electrode 13 a extending from the data line 13, drainelectrode 13 b and pixel electrode 15 connected to the drain electrode13 b. A storage capacitor 17 is provided for sustaining a charged liquidcrystal voltage and is formed by an overlap of the gate line 11 and thepixel electrode 15.

FIG. 2 provides a cross-sectional view of the related art LCD pixeltaken across a line I-I′ in FIG. 1 to illustrate details of an LCD pixelstructure. As shown in FIG. 2, a pixel TFT and capacitor are formed onthe substrate 21. The TFT includes a gate electrode 23. On the gateelectrode 23 and the substrate 21 is formed a gate insulating film 27.An amorphous silicon (a-Si) active layer 29 and a divided n⁺ layer 30are stacked on the gate insulating film 27 over the gate electrode 23. Asource electrode 32 and a drain electrode 34 are formed on the n⁺ layer30 and spaced from one another. Spaced from the TFT is a first electrode25 of the storage capacitor. The gate insulating film 27 extends overthe substrate 21 and covers the first storage capacitor electrode 25. Asecond electrode 25 a of the storage capacitor is formed on the extendedgate insulating film 27 over the first electrode 25 of the storagecapacitor. A passivation layer 36 is formed on the entire resultantsurface that includes the source electrode 32, the drain electrode and34, and the second electrode 25 a of the storage capacitor. A pixelelectrode 38 is formed on the passivation layer 36 an is connected tothe drain electrode 34 and the second electrode 25 a of the storagecapacitor through contact holes formed in the passivation layer 36.

Overlying the first substrate 21 is a second transparent substrate 21 a.On the second substrate 21 a, a black matrix (light shielding) layer 40and a color filter layer 42 are formed on the second substrate 21 a. Acommon electrode 44 is formed on an entire surface inclusive of thecolor filter layer 42 and the black matrix layer 40. A liquid crystallayer 100 is provided between the first substrate 21 and the secondsubstrate 21 a. However, a large step difference exists in the area ofthe substrate 21 where the storage capacitor Cs is formed. To compensatefor an unbalance caused by the difference in height around the area ofcapacitor Cs, spacers 101 and 103 are provided to restrict a gap betweenthe first substrate and the second substrate 21 a, and to maintain anappropriate thickness of the liquid crystal layer 100. The liquidcrystal layer 100 typically has a thickness of approximately 5 μm inareas of the pixel absent the steps formed by the capacitor Cs and theTFT. The spacers are plastic granules that are compressible by 10˜20% ofan uncompressed granule diameter.

The related art LCD of FIG. 2 shows how a step difference of 1.25 μm inthe area of storage capacitor Cs is compensated when it is desired thatthe liquid crystal layer 100 has a thickness of 5.1 μm in areas of thepixel where no step differences exist. Spacers 101 and 103 haveuncompressed diameters of approximately 4.75 μm. When the firstsubstrate 21 including the TFT and capacitor Cs and the second substrate21 a including the shielding layer 40, color filter layer 42 and thecommon pixel electrode 44 are arranged to provide the desired liquidcrystal thickness, the spacer 101 in the region of the storage capacitorCs is compressed approximately 20%. However, in the region outside areaof capacitor Cs, the spacer 103 is not compressed, and thus retains itsdiameter approximately 4.75 μm to allow for a balance of liquid crystalthickness in this region.

In the related art LCD, when a signal voltage is provided by a gatedriver (not shown) to the gate electrode 23 of the TFT, the TFT isturned on to provide a signal on the data line to the pixel electrode 38connected to the drain electrode 34. The signal provided to the pixelelectrode 38, together with a common voltage level (relative to thesignal on electrode 38) applied to common electrode 44, defines avoltage difference across electrodes 38, 44 to thereby charge the pixelcell. The liquid crystal layer 100 and the spacers 101 and 103 foradjusting the gap between the first and second substrates 21 and 21 aare located between the pixel electrode 38 and common electrode 44. Morespecifically, a signal voltage applied between the common electrode 44on the second substrate 21 a and the pixel electrode 38 on the firstsubstrate 21 controls the orientation of molecules of the liquid crystalbetween the electrodes to allow control of the transmissivity of lightthrough a liquid crystal cell in accordance with the applied voltage.

However, the related art LCD has the following problems. When the spacer101 in the region of the storage capacitor is compressed by 20% of itsdiameter, a 0.35 μm gap difference still remains between the regions ofthe pixel where no storage capacitor Cs is formed. In this case, thereis a thickness difference of the liquid crystal layer between a regionwhere a storage capacitor is formed and the regions surrounding thecapacitor. As a measure for accommodating height differences, spacers ofelastic granules are provided in the related art. However, the spacersof the related art cannot compensate for step differences that exceed anelastic range of the spacers. In this case, gaps form in parts of theliquid crystal layer causing in blurs and ripples on the screen andresulting in poor picture quality. Thus, there remains a need in the artfor LCD structures that compensate for step differences within panelsubstrates to maintain an effective gap for liquid crystal providedbetween the substrates.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a liquid crystaldisplay (LCD) that substantially obviates one or more of the problemsdue to limitations and disadvantages of the related art.

One aspect of the present invention is an LCD in which a heightdifference of a liquid crystal layer is compensated to form a uniformliquid crystal layer on an entire region.

Additional features and advantages of the invention will be set forth inthe description that follows, and in part will be apparent from thedescription, or may be learned by practice of the invention. Theobjectives and other advantages of the invention will be realized andattained by the structure particularly pointed out in the writtendescription, and claims hereof as well as the appended drawings.

To achieve these and other advantages in accordance with the presentinvention, as embodied and broadly described the liquid crystal displayincludes a first substrate, a thin film transistor and a storagecapacitor provided on the first substrate, a second substrate, a colorfilter layer on the second substrate and including a recess at alocation opposite to the storage capacitor, a common electrode on thecolor filter layer, and a liquid crystal layer including spacers betweenthe first and second substrates.

In another aspect of the present invention, a liquid crystal displaydevice includes a first substrate. A plurality of gate lines and aplurality of data lines are provided on the first substrate, and thedata lines cross the gate lines. A thin film transistor and a pixelelectrode are arranged at each intersections of the gate lines and datalines and a storage capacitor is defined by an overlap of one of thepixel electrodes and one of the plurality of gate lines. A black matrixlayer is formed on a second substrate opposite the first substrate forblocking transmission of light through parts of the liquid crystaldisplay excluding the pixel electrode. A color filter layer is formed onan substantially an entire surface of the second substrate inclusive ofthe black matrix layer and including a recess at a location opposite thestorage capacitor. A common electrode is formed on substantially anentire surface of the color filter layer, and a liquid crystal layerincluding spacers is formed between the first and second substrates.

In yet another aspect of the present invention, a display apparatusincludes a plurality of pixels arranged into a array between a firstsubstrate and a second substrate. Each of the plurality of pixelsdisplay a unit portion of an image corresponding to a data signal of aplurality of data signals. A first driver is provided for selectivityapplying the plurality of data signals along respective ones of aplurality of data lines provided on a first substrate. A plurality ofswitches are arranged into an array on a first substrate and areaddressable by control signals provided along a plurality of controllines on the first substrate. A second driver is provided forselectively applying the control signals to the control lines. A chargestoring capacitor is associated with each of the switches and isprovided on the first substrate. The capacitor stores charge provided byone of the data lines when the switch associated with the capacitor isdriven in an on state. Because each of the capacitors form a stepstructure on the first substrate, spacers are arranged between the firstand second substrates for maintaining a gap therebetween. The spacermeans are positioned over the step structure and in areas other thanover the step structure, and the second substrate includes compensatingmeans for accommodating at least a portion of the spacer over the stepstructure in correspondence with a height of the step to therebymaintain a substantially uniform cell gap.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention. In the drawings:

FIG. 1 provides a plan view illustrative of a layout of a related atLCD;

FIG. 2 illustrates a cross-sectional view of FIG. 1 taken along lineI-I′; and

FIG. 3 illustrates a section of an LCD in accordance with an exemplaryembodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings.

FIG. 3 is illustrative of a cross-section of an LCD in accordance with apreferred embodiment of the present invention. With reference to FIG. 3,the system that is formed on a first substrate 51 is substantiallyidentical to the system formed on the related art first substrate (shownin FIG. 2). However, the LCD structure of FIG. 3 is exemplary, i.e.,provided for illustrative purposes only, and it is to be understood thatthe present invention may be used in other LCD structures having stepsresulting from height differences on LCD substrate(s) between which aliquid crystal is provided.

As shown in. FIG. 3, a TFT and a capacitor Cs are formed on a firstsubstrate 51. The TFT include a gate electrode 53 formed on the firstsubstrate 51. A gate insulating film 57 is provided on the firstsubstrate 51 and on the gate electrode 53. An amorphous silicon (a-Si)active layer 59 and a divided n⁺ layer 60 are stacked on the gateinsulating film 57 and the gate electrode 53. A source electrode 62 anda drain electrode 64 are formed on the n⁺ layer 60 and spaced from eachother. The capacitor Cs includes a first electrode 55 that is also isformed on the first substrate 51 and spaced from the gate electrode 53.The gate insulating film is provided on the first electrode 55, and asecond electrode 55 a of the storage capacitor Cs is formed on the gateinsulating film 57 over the first electrode 55. A passivation layer 66is filmed on substantially an entire resultant surface that includes thesource and drain electrodes 62, 64, and the second electrode 55 a of thestorage capacitor. A pixel electrode 68 is formed on the passivationlayer 66 and is connected to the drain electrode 64 and the secondelectrode 55 a of the storage capacitor through contact holes providedin the passivation layer 66.

On a second substrate 51 a, a black matrix layer 70 may be provided atparts overlying areas excluding the pixel electrodes for preventing alight from transmitting through to elements on the substrate, such asthe TFTs, for example, whose operation may be adversely affected bytransmitted light. A color filter layer 72 is provided on the secondsubstrate 51 a, and a common pixel electrode 74 is provided on the colorfilter layer 72.

In the color filter layer 72 and the common pixel electrode 74, a recess73 is provided at a location opposite the storage capacitor Cs having adepth varied in accordance with the height difference caused by thestorage capacitor Cs. For example, when a height difference is ‘a’ μm,the depth of the recess may be formed to be within a range about ‘a’ μmto compensate for the height difference. Also, a similar recess may beformed in the color filter layer 72 and common pixel electrode 74 at alocation opposite the TFT.

A liquid crystal layer 200 is injected between the first substrate 51and second substrate 51 a of the foregoing LCD and includes spacers 201and 203 that are provided to control a gap between the substrates. Asshown in FIG. 3, the thickness of the liquid crystal layer in a regionincluding a storage capacitor Cs is substantially the same as in regionsthat do not include a storage capacitor. This effect is explained by theposition and depth of the recess 73 of the present invention within thestructure of the second substrate 51 a. The position of the spacer 201between an upper part of the storage capacitor Cs and the recess 73 inthe color filter layer 72 allows little or no compression of the spacer201 (such as in the case in the related art LCD due to lack of space).The spacer 201 thus maintains a diameter b or a diameter substantiallyidentical to the diameter b of the spacer 203 positioned in a regionother than, a region including a storage capacitor.

Even in a case when a height difference caused by the storage capacitorCs is greater than a range of spacer elasticity (e.g., approximately inthe range of 10˜20%), as the case may be, spacers with substantiallyidentical diameters may be applied to the region including the storagecapacitor Cs and in regions that do not include a storage capacitor,explained below in more detail.

Referring to FIG. 3, it is assumed that the liquid crystal layer 200 hasa thickness of 4.75 μm and the height difference caused by the storagecapacitor Cs is 1.25 μm. Of course, it is to be understood that thesedimensions are exemplary for the purpose of explaining the invention,i.e., the present invention may be practiced in other LCD's that requirea different liquid crystal layer thickness and/or include a differentheight difference. It also is to be understood that the depth of therecess 73 may be less than an amount that the spacer elasticity permitswithout adversely affecting the balance of the liquid crystal thickness.For example, a depth of the recess 73 may be less than the heightdifference “a” caused by the storage capacitor Cs as long as thedifference therebetween is within the compressible range of the spacer201.

In the exemplary embodiment described above, a balance in liquid crystalthickness is maintained between regions of the liquid crystal layer 200where the storage capacitor Cs is formed and where no storage capacitorCs is formed because the recess 73 is formed in the color filter layer72 to a depth of about 1.25 μm at a position opposite the storagecapacitor Cs. The recess 73 may be formed when forming the color filterlayer 72 or after the color filter layer 72 is formed.

In the LCD having the recess formed in the color filter layer 72 forcompensating the height difference caused by the storage capacitor Cs,when a signal is provided to the gate line 53, the TFT is turned on totransmit a signal on the data line to the pixel electrode 68. In otherwords, a liquid crystal cell can be operated by applying a signalvoltage between the common electrode 74 on the second substrate 51 a andthe pixel electrode 68 on the first substrate 51 to control orientationof the liquid crystal molecules between the two electrodes.

As should be clear from the embodiment described above, the LCD of thepresent invention compensates for a step that is formed by a storagecapacitor by providing a recess in a color filter layer. Even when aheight of the step exceeds an elastic range of spacers used to form agap between substrates, an overall thickness of the liquid crystal layercan be made substantially uniform to reduce blurs and/or ripples, andthereby provide an LCD capable of producing high picture quality.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the LCD of the presentinvention without departing from the spirit or scope of the invention.Thus, it is intended that the present invention cover the modificationsand variations of this invention provided they come within the scope ofthe appended claims and their equivalents.

What is claimed is:
 1. A liquid crystal display comprising: a firstsubstrate; a thin film transistor and a storage capacitor provided onthe first substrate; a second substrate; a color filter layer on thesecond substrate and including a recess at a location opposite to thestorage capacitor; a common electrode on the color filter layer; and aliquid crystal layer including spacers between the first and secondsubstrates.
 2. The liquid crystal display as claimed in claim 1, whereinthe recess has a depth corresponding to a height difference caused bythe storage capacitor over the first substrate.
 3. The liquid crystaldisplay as claimed in claim 1, wherein the spacers are elastic and haveapproximately the same diameter in an uncompressed state for ones of thespacers overlying a first region where the storage capacitor is locatedand ones of the spacers positioned in a second region that does notinclude the storage capacitor.
 4. The liquid crystal display as claimedin claim 2, wherein the height difference caused by the storagecapacitor is greater than an allowable elastic range of the spacers. 5.A liquid crystal display comprising: a first substrate; a plurality ofgate lines on the first substrate; a plurality of data lines on thefirst substrate, the data lines crossing the gate lines; a thin filmtransistor and a pixel electrode arranged at each intersection of thegate lines and data lines; a storage capacitor defined by an overlap ofone of the pixel electrodes and one of the plurality of gate lines; ablack matrix layer formed on a second substrate opposite the firstsubstrate for blocking transmission of light through parts of the liquidcrystal display excluding the pixel electrode; a color filter layerformed on an substantially an entire surface of the second substrateinclusive of the black matrix layer and including a recess at a locationopposite the storage capacitor; a common electrode formed onsubstantially an entire surface of the color filter layer; and a liquidcrystal layer including spacers formed between the first and secondsubstrates.
 6. The liquid crystal display as claimed in claim 5, whereinthe recess has a depth corresponding to a height difference caused bythe storage capacitor over the surface of the first substrate.
 7. Theliquid crystal display as claimed in claim 5, wherein ones of thespacers in a first region including the storage capacitor and ones ofthe spacers in a second region that does not include the storagecapacitor have substantially the same diameter.
 8. The liquid crystaldisplay as claimed in claim 6, wherein the height difference caused bythe storage capacitor is greater than an allowable elastic range of thespacer.